Asian Journal of Applied Science and Technology (AJAST) Page | 50

Volume 1, Issue 4, Pages 50-54, May 2017

Design and Fabrication of Lawn Mower

N.Nagarajan1, N.S.Sivakumar2 and R.Saravanan3
1Assistant Professor (Senior Grade), Department of Mechanical Engineering, Nehru Institute of Technology, Coimbatore, Tamilnadu, India.
2Assistant Professor, Department of Mechanical Engineering, Nehru Institute of Engineering and Technology, Coimbatore, Tamilnadu, India.
3Assistant Professor, Department of Mechanical Engineering, Nehru Institute of Engineering and Technology, Coimbatore, Tamilnadu, India.

Article Received: 27 April 2017 Article Accepted: 17 May 2017 Article Published: 20 May 2017

ABSTRACT

This project is to fabricate a grass cutter with helix shaped blade. At present grass cutter is operated by fuel and electrical energy. The design
objective is to come up with a mower that is portable, durable, easy to operate and maintain. In our project we fabricate the grass cutting machine for
the use of agricultural field, to cut the crops in the field. This is a new innovative concept mainly used in agricultural field. It is simple in construction
and its working is easy. The components that are used are wheel, gear arrangement, roller, bearing, and base frame. Below the gear arrangement
cutting blade is revolved. As the gear arrangement rotates the reel mover tends to cut the plants or crops. The reel consists of several helix shaped
blades mounted to a rotating shaft. The whole set up is placed on a movable base which has a wheel arrangement. It is used to maintain and upkeep
lawns in gardens, schools, college’s etc.
Keywords: Grass cutting machine, Components, Power supply, Sickle bar, Bevel gear and Cutting blade.

1. INTRODUCTION attached with a grass collector at the exit point. The blade is
The A lawn mower is an important equipment to maintain the seldom sharp enough to give a neat cutting. The blade simply
beauty of the lawn. The mower is with revolving blades to cut tears the grass resulting in brown tips. However, the
a lawn at an even length to make it good-looking. For the horizontal blades are easy to remove and sharpen or replace.
domestic purpose and in villages, people cannot spend more Existing engine trimmers suffer from high initial cost, high
money on heavy machineries. In villages there is more power levels of engine noise, high fuel consumption rates and high
cut problem and in these areas, this manual lawn mower used operator’s fatigue in long-run. For the installation of anchors
effectively. In market there are so many lawn mowers are technicians are more and more supported by manufacturers
available. It is not easy and also very difficult to maintain with descriptive technical manuals and in some cases with
uniform size. Hence we design to make a lawn mower without training courses.
any power source due to reduce the power consumption. The
blade removes the extra growth of the lawn and roller gives
light pressure to the top surface of Lawn. It gives fine look to
the lawn and uniform look throughout the Lawn. The cutting
mechanism is made of a flat blade rigidly fixed to the frame
behind the spiral arrangement which is configured to contact
at least one reel bar of the spiral blades during the rotation of
the spiral mechanism.

A traditional lawn mower is the height of the grass cut cannot

be adjusted spontaneously because the height adjustment of
the rotor blade is done by lifting the whole deck with the help
of wheel support and this mechanism takes time at least (4-5
minutes) to adjust the rotor. The components that are used are
motor, gear arrangement, cam, chain and sprocket, lead
screw, wheel, control unit. Below the gear arrangement
cutting blade is fixed. When the motor starts running by the
use of power supply, the shaft also rotates and that rotates the
gear arrangement which is coupled with the motor. Power
consumption becomes essential for future. Solar grass cutter
is a very useful device which is very simple in construction.
The most common types are fitted with wheels, but a newer
innovation is the hover model in which the spinning blade also
acts as a fan that provides a lift force, lifting the mower body
clear of the ground on the same principle with a hover craft.
Rotary mowers generally have opening by the side of the
housing through which cut grasses are expelled. Some are Fig. 1 Lawn mower-2D diagram
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Volume 1, Issue 4, Pages 50-54, May 2017

2. MECHANISM DESCRIPTION The blade is connected to the bevel gear. This gear train
Lawn mower is an essential tool for the maintenance of yards. increases the speed of the cutting blade. Shafts of the gears are
They vary in size, mode of operation, and human power. The connected to the bearings. The bearings are used for the shaft
power source riding mowers for example are usually powered stability and frictionless rotation. The lubricant is used for
by a gasoline engine and are ridden and steered by the bearings is ester oil. Straight bevel gear is used in this lawn
operator. It will walk behind mowers are designed to be mower because of its simple design and low speed. The
pushed by the operator and while getting the power from the cutting blade is a low lift blade used for the low speed.
wheel rotation. Modern gas powered and electric powered
lawn mowers cut grass with a single blade revolving at a high Wheel
speed parallel to the ground. In these method there is five Wheel is the mother part of all the components. Attached to
blades in cylinder is rotating and achieving the same power the axle and used to move the entire system.The main wheels
given by the operator. The blade is slightly raised along its are the contact point with the ground. The ring gear having 63
rear edge to create draft that lifts the cutting blades before its teeth and it is covered by the frame need of protection. The
cutting operation. circular diameter of wheel is 200 mm. Tire is covered outer
side of the wheel which gives the grip on wheel rotation.
Terminology
The attitude refers to the angle of the bed knife. This reference
is in degree differential from the surface of the turf, (or the
line intersecting the bottom of the rollers).The shear point is
the point that a reel blade contacts any given point on the bed
knife at a specific point in time. The reel centerline, is the
imaginary line drawn perpendicular to the grass dissecting the
reel at its center.

This line is used to find the Behind Center Distance (BCD),

this is the distance the shear point lies behind the centerline.
There are two rollers. The rear roller trails the cutting unit,
and is usually a solid roller.

Some cutting units have a fixed by screws, and the rear roller Fig.3 2D- Diagram for wheel
is used to set the height of cut. Others, such as the newer DPA
design cutting units, have a fixed rear roller, and the front
roller is used to set the height of cut.

Fig.4 Spiral cutter

Spiral Cutter
The spinning blades of the mower do not actually cut the
grass. It manipulates the grass to be cut by the cutter blade or
Fig.2. Grass cutting on bed knife bed knife. The cutting surface shears the grass as it is caught
between the spinning drum and the cutter blade. A reel mower
The performance of the machine was evaluated through a cuts grass with a scissors like shearing action, as the moving
field test. A land predominantly covered with carpet grass was helix shaped blades pass over the stationary bed knife. The
mapped out into plots of 4mx2m. Seven of these plots were cutting action requires that the bed knife and reel blades
selected by randomization process and mowed. The spiral matched, and in close relationship with each other. This weld
lawn mower uses multiple cutting blades arranged in form of a is then ground to be a perfect cylinder. The reel is supported
cylinder which is turned by a gear connected to the wheels. by precision bearings held within the side plates. The side
The act of pushing the machine makes the cylinder revolve. plates are held in place by a frame. This becomes the reel
assembly, and is a precision cutting tool. The reel assembly is
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Volume 1, Issue 4, Pages 50-54, May 2017

supported by rollers, and pulled along the ground by a carrier Mechanism

frame. Everything comes together, to make a precision cutting A mechanism is a device designed to transform input forces
tool. and movement into a desired set of output forces and
movement. The internal spur gear is transfers the torque to the
The spinning blades of the mower do not actually cut the cutter cylinder by gear engagement. The cutting mechanism is
grass. It manipulates the grass to be cut by the cutter blade or made of a flat blade rigidly fixed to the frame. Mechanisms
bed knife. The reel consists of five or six helix shaped blades, generally consist of moving components such as gears and
welded to supports and mounted to a shaft. This weld is then gear trains, belt and chain drives, cam and follower
ground to be a perfect cylinder. The reel is supported by mechanisms, and linkages as well as friction devices such as
precision bearings held within the side plates. The side plates brakes and clutches, and structural components such as the
are held in place by a frame. frame, fasteners, bearings, springs, lubricants and seals, as
well as a variety of specialized machine elements such as
This becomes the reel assembly, and is a precision cutting splines, pins and keys.
tool. The reel assembly is supported by rollers, and pulled
along the ground by a carrier frame. Everything comes 3. MATERIAL USED
together, to make a precision cutting tool. Mild steel

Bed Knife
The bed knife is held rigidly in position on the bed bar by
screws. The bed knife is sharpened to be flat and square so the
sharp edge contacts the reel blades across the entire length. If
the bed knife is not flat, or the reel is not a perfect cylinder, it
is impossible to get the bed knife to contact along the entire
length of the reel. The contact between the blade reel and
cutter blade provides a shearing force which cuts the grass. It
consists of a horizontal knife screwed to bed knife bar.

Spur Gear
The lawn mower shall be driven from both wheels with
suitable ratchet action provided on both sides between the
drive wheels and cutting reel. Gears and pinions shall mesh
fully and smoothly. Fig.6. Mild steel

Wear of material
Wear is commonly defined as the undesirable
deterioration of a component by the removal of material
from its surface. It occurs by displacement and detachment
of particles from surface. The mechanical properties of steel
are sharply reduced due to wear. The wear of material may be
due to the friction of metals against each other, eroding
effect of liquid and gaseous media, scratching of solid
particles from the surface and other surface phenomena.
There are following principle types of wear as described
below.

Abrasive wear
It results when nonmetallic particles penetrate the metal
surface and Cause removal of metallic debris.
Fig.5 Spur Gear
Adhesive wear or metal to metal wear
Spur gears or straight-cut gears are the simplest type of gear. This wear caused due to relatives sliding or rolling
They consist of a cylinder or disk with the teeth projecting movement of two mating metallic surfaces.
radically, and although they are not straight-sided in form of
the edge of each tooth is straight and aligned parallel to the Erosive wear
axis of rotation. Erosive wear occur as a result of relative movement
between metal and liquid or gas.
Geared devices can change the speed, torque, and direction of
a power source. The term is used to describe similar devices Corrosive wear
even when the gear ratio is continuous rather than discrete, or The destruction of materials by the action of surrounding
when the device does not actually contain any gears, as in a medium is called corrosion.
continuously variable transmission.
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Volume 1, Issue 4, Pages 50-54, May 2017

4. DESIGN CALCULATION

1. Gear calculation

Fabrication and Working

The conceptual design report highlights the design process
used for this project. This report contains useful information
with regards to the thought process and techniques used in
analysing alternative solutions. The background and context
for this project are discussed in detail in this report. The
requirements that have been defined were established by
doing market research and examining the problems that arise
while using a manual mower. Basic and technical
requirements have been defined for the project.

Basic requirements include physical characteristics such as

weight and dimensions. These are fundamental to the safe and
efficient operation of the mower. Technical requirements
have been defined after initial calculations. A battery powered
reel mower would separate the rotation of the blade reel from
the rotation of the wheels, allowing the drum to spin faster and
making it less susceptible to jamming. Reel mowers also cut
lawns more evenly and much closer.
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Asian Journal of Applied Science and Technology (AJAST) Page | 54
Volume 1, Issue 4, Pages 50-54, May 2017

Working If the reel speed is too fast, in relation to groundspeed, the

Working of the lawnmower is depending on the wheel leaves of the grass plants impacted multiple times before
rotation. Wheel is the main component of this machine. The being cut.
rotation is transferred from wheel to the spider by gear
engagement. Also the rotation of the spider is controlled in 5. CONCLUSION
one direction by the ratchet mechanism. It is placed on the The progress in science & technology is a non-stop process.
pinion inside. New things and new technology are being invented. As the
technology grows day by day, we can imagine about the future
Rotating spider is strike the bed knife and the grass is sheared in which thing we may occupy every place. The proposed
to applied level of cutting height. Maintenance of the height of system is found to be more compact, user friendly and less
cut is done using support rollers. complex, which can readily be used in order to perform
several tedious and repetitive tasks. The spiral blade lawn
mower was designed, fabricated and tested. This does not
have engine and is powered by the operator. Test revealed
that, higher grass cutting efficiency is obtained when the lawn
is dry before mowing. The machine is simply powered by
manual pushing. Therefore, it can be used by both rural as
well as urban dwellers. It is also affordable since the cost of
production is low. High moisture content and undulated
nature of the field surface affected the efficiency of the
machine.The principle of the development of science is that
“nothing is impossible”. So we shall look forward to a bright
& sophisticated world.

The spiral blade lawn mower was designed, fabricated and

tested. This does not have engine and is powered by the
operator. Test revealed that, higher grass cutting efficiency is
obtained when the lawn is dry before mowing. The machine is
Fig.7 Grass cutting simply powered by manual pushing. Therefore, it can be used
by both rural as well as urban dwellers. It is also affordable
Reel mowers also cut lawns more evenly and much closer. since the cost of production is low. High moisture content and
The cylindrical drum on a reel mower cuts every individual undulated nature of the field surface affected the efficiency of
blade of grass like a pair of scissors. This produces a clean the machine. Effort should be made to adopt and popularize
cut, which will protect the grass from disease and increases this design especially for the benefits of rural people who
the health of the grass. Optimum clip rate is achieved when make up a great percentage of the nation’s population. It is
the bed knife and reel blades create small, even gatherings also hoped that, when mass produced, the unit cost will be
that are then cut. The result is a small, unnoticeable clip and reduced. The spiral blade lawn mower is environmental
an even after cut appearance. friendly.

REFERENCES
[1] Khurmi, R.S. and Gupta, J.K. (2003). Machine Design.
Eurasa Publishing House, Ltd. New Delhi, India.

[2] Shigley. J.E. and Mischk.C.R (2001). Mechanical

Engineering Design. Mc-Graw Hill Co. Inc. New York.

[3] Yong and Chow, S.H. (1991). Design and Construction of

an Improved Domestic Lawn Mower. Project Report; Beijing
Institute of Technology, China.

[4] Desa Ahmad, “A Width of Cut Analysis on the

Performance of a Rotary Strip Tiller”, Pertanika Vol. 9 No. I,
1986.

Fig.8 Clip rate-High speed condition [5] Mohd Ishammudin Bin Mohd Yunus, “Design and
Development of Grass Cutting Machine Using DFMA
If the reel speed is too slow in relation to the groundspeed, Methodology”, University Teknikal Malaysia Melaka,
there is too much space between cuts, resulting in visible clip 2007/2008.
marks and uncut grass. Visible clip marks in the turf are the
result of an incorrect clip rate.

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